IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
In re International Application of
Sadayuki ABETA, Mamoru SAWAHASHI and Fumiyuki ADACHI
International Serial No.: PCT/JP99/02154
International filing date: April 22, 1999
For: CDMA RECEIVER AND CDMA TRANSCEIVER
VERIFI CATION OF TRANS T ■ A T T r>M
Honorable Commissioner of Patent and Trademark
Washington, D.C. 20231
Sir:
Masashi SHINKAI residing at c/o TANI & ABE, No. 6-20,
Akasaka 2-chome, Minato-ku, Tokyo 107-0052, Japan,
declares:
(1) that he knows well both the Japanese and
English languages;
(2) that he translated the claims of the above-
identified International Application from Japanese to
English;
(3) . that the attached English translation is a
true and correct translation of the claims, specification
and drawings of the above-identified International
Application to the best of his knowledge and belief; and
(4) that all statements made of his own
knowledge are true and that all statements made on
information and belief are believed to be true, and further
that these statements are made with the knowledge that
willful false statements and the like are punishable by
fine or imprisonment, or both, under 18 USC 1001, and that
such false statements may jeopardize the validity of the
application or any patent issuing thereon.
December 3, 1999 7K , ^Ul>J^
Date Masashi SHINKAI
7 J
SPECIFICATION
TITLE OF THE INVENTION
CDMA RECEIVER AND CDMA TRANSCEIVER
5
TECHNICAL FIELD
The present invention relates to a CDMA (Code
Division Multiple Access) receiver and a CDMA
transceiver which have high resistance to fading
10 fluctuations, and carry out highly accurate channel
estimation, considering the rate of channel
fluctuations (propagation path fluctuations) .
BACKGROUND ART
15 In a mobile communication environment,
fluctuations in amplitude and phase can take place
in a propagation channel because of Rayleigh fading
caused by variations in relative locations of a
mobile station and a base station. Therefore, it is
20 common for a conventional phase modulation method
which transmits data (information) by carrier phase
to impose data on relative phases of successive
symbols by differential encoding on a transmitting
side, and to make identification and decision of the
25 data by differential detection on a receiving side.
- 1 -
%
In the differential detection, however, one bit
error in a radio section causes two bit error
because the data to be transmitted is modulated with
the differential encoding as mentioned above. Thus,
5 under the same SNIR (Signal to Noise and
Interference power Ratio) , the received error rate
will increase by 3 dB from that of the coherent
detection such as binary phase shift keying (BPSK) .
On the other hand, although the coherent
10 detection that decides the phase of a received
signal for each data symbol by the absolute phase
has highly efficient receiving characteristics, it
is difficult to decide the received absolute phase
in a Rayleigh fading environment.
15 To solve the problem, a method is proposed that
insert pilot symbols into a data symbol sequence,
and carries out channel estimation of the data
symbols using the pilot symbols. As a pilot symbol
insertion method, there are a time multiplexed pilot
20 channel method that inserts pilot symbols between
data symbols, and a parallel pilot channel method
that inserts pilot symbols in parallel with data
symbols.
The following references 1-3 propose a channel
25 estimation method based on the time multiplexed
pilot channel method.
- 2 -
S
Reference 1: Seiichi Sampei and Terumi Sunaga,
"Rayleigh Fading Compensation for QAM in Land Mobile
Radio Communication", IEEE Trans. Vehicular Technol .
VT-42, No. 2, May 1993. It proposes a method of
5 estimating and compensating for the fading
distortion using pilot symbols that are inserted
between data symbols at fixed intervals and have
known phases. In this method, a pilot symbol is
inserted at every several data symbol intervals, and
10 the channel estimation is carried out based on the
received phases of the pilot symbols. In other
words, it measures the amplitude and phase of the
received signal of each path of each user at the
pilot symbols before and after the current data
15 symbol section, and estimates the channel
fluctuations in the data symbol section by
interpolating the measured values.
Reference 2: Hidehiro Ando et.al, "Channel
Estimation Filter Using Time -Multiplexed Pilot
20 Channel for Coherent RAKE Combining in DS-CDMA" ,
Mobile Radio, IEICE Trans. Commun. V0I.8I-B, No. 7,
July 1998. It proposes a method of carrying out
more highly accurate channel estimation by making
channei estimation using more pilot symbols.
25 Fig. 23 is a diagram illustrating a channel
estimation method based on the reference 2. In this
- 3 -
method, the transmission power control is carried
out at every slot interval to follow instantaneous
Rayleigh fluctuations. Therefore, as illustrated in
Fig. 23, the amplitude (power) of the combined
5 symbol sequence of data symbols and pilot symbols
varies at every slot interval, and the phase also
varies slightly due to the operation of an amplifier
during transmission. Such transmission power
control enables a reverse channel of the DS-CDMA
10 (Direct Sequence CDMA) to secure the SNIR against
interference signals caused by cross-correlation
with other users.
The channel estimation of the data symbols is
performed using pilot symbols inserted between data
15 symbols at fixed intervals. Specifically, it is
carried out by averaging (taking coherent sums of)
pilot symbols (estimated complex fading envelopes)
in a plurality of slots before and after the slot,
to which the data symbols to be subjected to the
20 channel estimation belong, and by obtaining a
channel estimation value £ by taking the weighted
sum (weighted average) of the average values £ using
weighting factors 0to, (Xi and so on, thereby
achieving highly accurate channel estimation.
- 4 -
Using many pilot symbols belonging to different
slots enables highly accurate channel estimation.
This is because in an actual mobile propagation
environment, interference signals, which are
5 generated by thermal noise (to minimize the
transmission power, a noise limited environment is
created particularly at cell edges) , and by cross-
correlation from other users, are added to the
desired signal of the current channel, and the
10 channel estimation accuracy is degraded because of
the phase and amplitude of the received signal that
vary at every moment due to fading. Although the
pilot symbols in different slots have different
power, the channel estimation error due to the power
15 difference is less than the reduction effect by the
thermal noise and interference signals caused from
using pilot symbols in more slots.
The reference 2 method assumes that the channel
fluctuations in each slot are small, and employs the
20 same weighting factors a for all the data symbols in
each slot to obtain the same channel estimation
value £. This presents a problem of impairing the
characteristics in high rate fading.
Reference 3, Sadayuki Abeta et.al, "Performance
25 Comparison between Time-Multiplexed Pilot Channel
- 5 -
and Parallel Pilot Channel for Coherent Rake
Combining in DS-CDMA Mobile Radio", IEICE Trans.
Commun. V0I.8I-B, No. 7, July 1998. It proposes a
method of achieving highly accurate channel
5 estimation in making channel estimation of the data
symbols by obtaining a channel estimation value by
appropriately taking weighted sum of the pilot
symbols in a plurality of slots before and after the
slot, to which the current data symbols belong,
10 using appropriate weighting factors for each data
symbol in the same- slot (weighting factors a m , 0 , Ot m ,i
and so on for m-th data symbol in the slot) . First
to fourth embodiments in accordance with the present
invention apply this scheme (see, Fig. 3) .
15 For example, in Fig. 23, for the (m-A)-th data
symbol in the n-th slot, where A is a natural
number, the pilot symbols in the n-th slot are
assigned a greatest weight. This is because the
pilot symbols in the n-th slot are closest (in time)
20 to the (m-A)-th data symbol, and hence best reflect
the channel state when receiving the data symbols .
In contrast, for the (m+B)-th data symbol in the n-
th slot, where B is a natural number, the pilot
symbols in the (n+l)-th slot are assigned a greatest
25 weight. This is because the pilot symbols in the
(n+l)-th slot are closest (in time) to the (m+B) -th
- 6 -
data symbol, and hence best reflect the channel
state when receiving the data symbols.
As for the parallel pilot channel method, the
following reference 4 and the foregoing reference 3
disclose a channel estimation method based on the
method .
Reference 4, Sadayuki Abeta et.al, "DS/CDMA
Coherent Detection System with a Suppressed Pilot
Channel", IEEE GLOBECOM'94, pp. 1622-1626, 1994. it
proposes a method of estimating and compensating for
the fading distortion by inserting pilot channel
having known phase in parallel with and
perpendicular to the data channel for transmitting
data .
The channel estimation of the data symbols is
carried out by averaging the pilot symbols in a
section to which the target data symbol belongs, and
by obtaining the channel estimation value. Thus,
the channel estimation with high SNIR is achieved.
By using the estimation value, the received signal
in each path of each user is detected at the
positions of the pilot symbols in the current data
symbol section, and the amplitude and phase
measurement is carried out for the signal of each
path so as to estimate and compensate for the
channel fluctuations in the data symbol section.
When performing the channel estimation of the
data symbols in the reference 4 method, the average
of the pilot symbols is calculated only within the
slot including the target data symbol, and the
average is made the channel estimation value.
The foregoing reference 3 proposes a method of
achieving more highly accurate channel estimation by
obtaining a more highly accurate channel estimation
value by taking weighted sum of the pilot symbols
appropriately when carrying out the channel
estimation of the data symbols. This method is
applied to the fifth to eighth embodiments in
accordance with the present invention (see, Fig.
14) .
Fig. 14 illustrates the channel estimation
method disclosed by the reference 3. In Fig. 14,
the channel estimation is carried out using a pilot
symbol sequence parallel to the data symbol
sequence. Specifically, it obtains the channel
estimation value £ by generating a plurality of
pilot blocks from the pilot symbols, by averaging
the pilot symbols in each of the pilot blocks, and
by taking a weighted sum of the average values £
using weighting factors cti, <x_i and so on, thereby
achieving highly accurate channel estimation. Using
many pilot symbols belonging to different slots in
carrying out the channel estimation enables the
highly accurate channel estimation.
To suppress the power loss, the power of the
5 pilot symbol sequence is set less than that of the
data symbol sequence. In addition, to follow the
instantaneous Rayleigh fluctuations, the
transmission power control is performed at every
slot interval. This enables the reverse channel in
10 the DS-CDMA to secure the SNIR against the
interference signals caused by the cross-correlatio
from other users.
The methods disclosed in the foregoing
references 3 and 4, however, use constant weighting
15 values regardless of the fading fluctuations. This
presents a problem in that when setting optimum
weighting values for low rate fading fluctuations,
the highly accurate channel estimation cannot be
achieved in the high rate fading, whereas when
20 setting optimum weighting values for high rate
fading fluctuations, the highly accurate channel
estimation cannot be achieved in the low rate
fading.
25 DISCLOSURE OF THE INVENTION
- 9 -
The present invention is implemented to solve
the foregoing problems. It is therefore an object
of the present invention to improve the resistance
to fading fluctuations and to carry out the highly
accurate channel estimation by adaptively optimizing
the weighting values for the pilot symbols in
response to the rate of channel fluctuations.
Achieving highly accurate channel ' estimation and
compensation of channel fluctuations of data symbols
based on the channel estimation makes it possible to
decide the absolute phase of each data symbol under
a Rayleigh fading environment using the coherent
detection, and to reduce the SNIR required for
obtaining a predetermined level of receiving quality
(receiving error rate). Therefore, the transmission
power can be reduced, and the capacity in terms of
the number of users of the system can be increased.
In order to accomplish the object
aforementioned, according to the invention as
claimed in claim 1, a CDMA receiver for receiving
and demodulating a signal including a combined
symbol sequence that has a plurality of slots and
includes data symbols and pilot symbols, comprises:
means for detecting positions of the pilot
symbols in the combined symbol sequence;
- 10 -
means for generating pilot blocks by extracting
in a plurality of slots the pilot symbols from the
combined symbol sequence in response to a result of
the detection;
means for obtaining channel estimation values by
calculating a weighted sum of average values of the
pilot symbols in the pilot blocks;
means for acquiring from the combined symbol
sequence a data symbol sequence in accordance with
the result of the detection;
means for compensating for channel fluctuations
of the data symbol sequence using the channel
estimation values; and
means for controlling the weighting in response
to a rate of the channel fluctuations.
According to the invention as claimed in claim
2, in the CDMA receiver as claimed in claim 1, the
means for controlling the weighting comprises:
means for compensating for, using the channel
estimation values, channel fluctuations of a pilot
symbol sequence extracted from the combined symbol
sequence;
means for generating an error signal from the
compensated pilot symbol sequence and an ideal pilot
symbol sequence ; and
means for carrying out the weighting control
using the error signal and the average values of the
pilot symbols included in the pilot blocks.
According to the invention as claimed in claim
3, in the CDMA receiver as claimed in claim 1, the
means for controlling the weighting comprises:
means for generating an error signal from the
compensated data symbol sequence and from result
obtained by demodulating and deciding the
compensated data symbol sequence; and
means for carrying out the weighting control
using the error signal and the average values of the
pilot symbols included in the pilot blocks.
According to the invention as claimed in claim
4, in the CDMA receiver as claimed in claim 1, the
means for controlling the weighting carries out the
weighting control using as update values inner
products of the channel estimation values of the
data symbols and the average values of the pilot
symbols included in the pilot blocks.
According to the invention as claimed in claim
5, in the CDMA receiver as claimed in any one of
claims 1-4, the CDMA receiver receives a signal
including a combined symbol sequence having a frame
structure consisting of slots in which the pilot
symbols consisting of a few symbols are inserted
- 12 -
into the data symbol sequence at every fixed
interval .
According to the invention as claimed in claim
6, in the CDMA receiver as claimed in any one of
claims 1-5, the pilot blocks are formed from all the
pilot symbols in a slot.
According to the invention as claimed in claim
7, in the CDMA receiver as claimed in any one of
claims 1-6, when obtaining the channel estimation
value of a data symbol in an n-th slot of the
combined symbol sequence, where n is an integer, the
pilot blocks are generated from an (n-K+l)-th slot
to an (n+K)-th slot of the combined symbol sequence,
where K is a natural number.
According to the invention as claimed in claim
8, a CDMA receiver for receiving and demodulating a
signal including a data symbol sequence and a pilot
symbol sequence parallel to the data symbol
sequence, comprises:
means for generating a plurality of pilot blocks
from the pilot symbol sequence;
means for obtaining channel estimation values by
calculating a weighted sum of average values of the
pilot symbols in the pilot blocks;
- 13 -
means for compensating for channel fluctuations
of the data symbol sequence using the channel
estimation values; and
means for controlling the weighting in response
to a rate of the channel fluctuations.
According to the invention as claimed in claim
9, in the CDMA receiver as claimed in claim 8, the
means for controlling the weighting comprises:
means for compensating for, using the channel
estimation values, channel fluctuations of the pilot
symbol sequence;
means for generating an error signal from the
compensated pilot symbol sequence and an ideal pilot
symbol sequence; and
means for carrying out the weighting control
using the error signal and the average values of the
pilot symbols included in the pilot blocks.
According to the invention as claimed in claim
10, in the CDMA receiver as claimed in claim 8, the
means for controlling the weighting comprises:
means for generating an error signal from the
compensated data symbol sequence and from result
obtained by demodulating and deciding the
compensated data symbol sequence; and
- 14 -
means for carrying out the weighting control
using the error signal and the average values of the
pilot symbols included in the pilot blocks.
According to the invention as claimed in claim
11, in the CDMA receiver as claimed in claim 8, the
means for controlling the weighting carries out the
weighting control using as update values inner
products of the channel estimation values of the
data symbols and the average values of the pilot
symbols included in the pilot blocks.
According to the invention as claimed in claim
12, in the CDMA receiver as claimed in any one of
claims 8-11, the CDMA receiver receives a signal
including a data symbol sequence which is spread
using a first spreading code, and a pilot symbol
sequence which is parallel to the data symbol
sequence and spread using a second spreading code,
the first spreading code and the second spreading
code being orthogonal to each other.
According to the invention as claimed in claim
13, in the CDMA receiver as claimed in any one of
claims 8-12, the CDMA receiver receives a signal
including a spread data symbol sequence which is
impressed on a first carrier, and a spread pilot
symbol sequence which is parallel to the data symbol
sequence and is impressed on a second carrier, the
first carrier and the second carrier being
orthogonal to each other.
According to the invention as claimed in claim
14, in the CDMA receiver as claimed in any one of
5 claims 8-13, when obtaining the channel estimation
value of an n-th data symbol in the data symbol
sequence, where n is an integer, the plurality of
pilot blocks are generated from an (n-K+l)-th pilot
symbol to an (n+K)-th pilot symbol in the pilot
10 symbol sequence, where K is a natural number.
According to the invention as claimed in claim
15, in the CDMA receiver as claimed in any one of
claims 8-14, the plurality of pilot blocks have a
same length.
15 According to the invention as claimed in claim
16, a CDMA transceiver includes a transmitting
section for transmitting a signal including a
combined symbol sequence that has a plurality of
slots and includes data symbols and pilot symbols,
20 and a receiving section for receiving and
demodulating the signal, and the receiving section
comprises :
means for detecting positions of the pilot
symbols in the combined symbol sequence;
25 means for generating pilot blocks by extracting,
in a plurality of slots, the pilot symbols from the
- 16 -
combined symbol sequence in response to a result of
the detection;
means for obtaining channel estimation values by
calculating a weighted sum of average values of the
5 pilot symbols included in the pilot blocks;
means for acquiring from the combined symbol
sequence a data symbol sequence in accordance with
the result of the detection;
means for compensating for channel fluctuations
10 of the data symbol sequence using the channel
estimation values; and
means for controlling the weighting in response
to a rate of the channel fluctuations.
According to the invention as claimed in claim
15 17, a CDMA transceiver includes a transmitting
section for transmitting a signal including a data
symbol sequence and a pilot symbol sequence parallel
to the data symbol sequence, and a receiving section
t
for receiving and demodulating the signal, and the
20 receiving section comprises:
means for generating a plurality of pilot blocks
from the pilot symbol sequence;
means for obtaining channel estimation values by
calculating a weighted sum of average values of the
25 pilot symbols in the pilot blocks;
- 17 -
means for compensating for channel fluctuations
of the data symbol sequence using the channel
estimation values; and
means for controlling the weighting in response
to a rate of the channel fluctuations.
According to the invention as claimed in claim
18, a CDMA receiving method of receiving and
demodulating a signal including a combined symbol
sequence that has a plurality of slots and includes
data symbols and pilot symbols, comprises the steps
of:
detecting positions of the pilot symbols in the
combined symbol sequence ;
generating pilot blocks by extracting, in a
plurality of slots, the pilot symbols from the
combined symbol sequence in response to a result of
the detection;
obtaining channel estimation values by
calculating a weighted sum of average values of the
pilot symbols in the pilot blocks;
acquiring from the combined symbol sequence a
data symbol sequence in accordance with the result
of the detection; and
compensating for channel fluctuations of the
data symbol sequence using the channel estimation
value,
wherein the weighting is controlled in response
to a rate of the channel fluctuations.
According to the invention as claimed in claim
19, a CDMA receiving method of receiving and
demodulating a signal including a data symbol
sequence and a pilot symbol sequence parallel to the
data symbol sequence, comprises the steps of:
generating a plurality of pilot blocks from the
pilot symbol sequence;
obtaining channel estimation values by
calculating a weighted sum of average values of the
pilot symbols in the pilot blocks; and
compensating for channel fluctuations of the
data symbol sequence using the channel estimation
value,
wherein the weighting is controlled in response
to a rate of the channel fluctuations.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram showing a
configuration of a CDMA receiver of a first
embodiment in accordance with the present invention;
Fig. 2 is a diagram showing relationship between
Figs. 2 A and 2B;
Fig. 2A is a flowchart illustrating a receiving
processing by the CDMA receiver of the first
embodiment in accordance with the present invention;
Fig. 2B is a flowchart illustrating the
receiving processing by the CDMA receiver of the
first embodiment in accordance with the present
invention;
Fig. 3 is a diagram illustrating the operation
principle of the channel estimation by the CDMA
receiver of the first embodiment in accordance with
the present invention, taking an example of the
channel estimation;
Fig. 4 is a flowchart illustrating a weighting
control processing by the CDMA receiver of the first
embodiment in accordance with the present invention;
Fig. 5 is a block diagram showing a
configuration of a CDMA transceiver of a second
embodiment in accordance with the present invention;
Fig. 6 is a block diagram showing a
configuration of a transmission processor of the
CDMA transceiver in the second embodiment in
accordance with the present invention;
Fig. 7 is a flowchart illustrating a
transmission processing by the transmission
processor of the CDMA transceiver in the second
embodiment in accordance with the present invention;
- 20 -
Fig . 8 is a block diagram showing a
configuration of the CDMA receiver of a third
embodiment in accordance with the present invention;
Fig. 9 is a flowchart illustrating a weighting
control processing by the CDMA receiver of the third
embodiment in accordance with the present invention;
Fig. 10 is a block, diagram showing a
configuration of the CDMA receiver of a fourth
embodiment in accordance with the present invention;
Fig. 11 is a flowchart illustrating a weighting
control processing by the CDMA receiver of the
fourth embodiment in accordance with the present
invention;
Fig. 12 is a block diagram showing a
configuration of the CDMA receiver of a fifth
embodiment in accordance with the present invention;
Fig. 13 is a diagram showing relationship
between Figs. 13A and 13B;
Fig. 13A is a flowchart illustrating a receiving
processing by the CDMA receiver of the fifth
embodiment in accordance with the present invention;
Fig. 13B is a flowchart illustrating the
receiving processing by the CDMA receiver of the
fifth embodiment in accordance with the present
invention;
Fig. 14 is a diagram illustrating the operation
principle of the channel estimation by the CDMA
receiver of the fifth embodiment in accordance with
the present invention, taking an example of channel
5 estimation;
Fig. 15 is a block diagram showing a
configuration of a CDMA transceiver of a sixth
embodiment in accordance with the present invention;
Fig. 16 is a block diagram showing a
10 configuration of a transmission processor of the
CDMA transceiver in the sixth embodiment in
accordance with the present invention;
Fig. 17 is a flowchart illustrating a
transmission processing by the transmission
15 processor of the CDMA transceiver in the sixth
embodiment in accordance with the present invention ;
Fig. 18 is a block diagram showing a
configuration of the CDMA receiver of a seventh
embodiment in accordance with the present invention;
20 Fig. 19 is a block diagram showing a
configuration of the CDMA receiver of an eighth
embodiment in accordance with the present invention;
Fig. 2 0 is a diagram illustrating required error
rate (BER=10" 3 ) characteristics for the product of a
25 slot time (T s i ot ) and a maximum Doppler frequency
(fd) under a two-path Rayleigh model;
- 22 -
Fig. 21 is a diagram illustrating BER
characteristics under a Vehicular-B environment when
fdT s lot=0. 003125 and f dT s lot=0 . 28 ;
Fig. 22 is a diagram showing required error rate
5 (BER=10" 3 ) characteristics for fdT s lot under a
Vehicular-B environment; and
Fig. 2 3 is a diagram illustrating the operation
principle of channel estimation in accordance with a
related art.
10
BEST MODE FOR CARRYING OUT THE INVENTION
The best mode for carrying out the invention
will now be described with reference to the
accompanying drawings .
15 First to fourth embodiments in accordance with
the present invention relates to a CDMA receiver or
a CDMA transceiver based on the time multiplexed
pilot channel method, and fifth to eighth
embodiments in accordance with the present invention
20 relates to a CDMA receiver or a CDMA transceiver
based on the parallel pilot channel method.
[FIRST EMBODIMENT]
Fig. 1 is a block diagram showing a
configuration of a CDMA receiver of a first
25 embodiment in accordance with the present invention.
The CDMA receiver 100 of the present embodiment
- 23 -
receives and demodulates a signal including a
combined symbol sequence that has a plurality of
slots and includes data symbols and pilot symbols.
The CDMA 1 receiver 100 comprises a receiving
section 110, a matched filter 125, a slot
synchronization detector 101, a pilot symbol
sequence acquisition section 112, a pilot block
generator 111, a channel estimation value
acquisition section 121, a data symbol sequence
acquisition section 129, a data symbol sequence
compensator 130, a RAKE combiner 132, an error
signal generator 142, and a weighting controller
(MMSE) 144. Although in the present embodiment, the
matched filter 125, slot synchronization detector
101 and the like are implemented by software using a
DSP (Digital Signal Processor) (plus a memory for
storing programs) 120 as shown in Fig. 1, they can
be implemented by means of hardware, in which case
delay circuits and other components are used as
needed.
Figs. 2A and 2B are a flowchart illustrating a
receiving processing by the CDMA receiver of the
present embodiment. First, at step S201, the
receiving section 110 receives a receiving signal,
that is, a spread combined symbol sequence. At step
S202, the matched filter 125 despreads the received
signal to generate a combined symbol sequence.
Subsequently, at steps S203-S208, the slot
synchronization detector 101, pilot symbol sequence
acquisition section 112, pilot block generator 111
5 and channel estimation value acquisition section 121
carry out the channel estimation processing, thereby
acquiring channel estimation values of the data
symbols and pilot symbols.
Fig. 3 is a diagram illustrating the operation
10 principle of the channel estimation by a channel
estimation unit of the present embodiment by way of
example of acquiring channel estimation values of an
m-th data symbol in n-th slot, where n and m are
integers . The combined symbol sequence in the
15 example as shown in Fig. 3 is subjected to the
transmission power control at every slot interval.
Each slot of the combined symbol sequence has a form
in which a fixed length pilot symbols are followed
by a fixed length data symbols. In other words, the
20 combined symbol sequence has a frame structure in
which a unit of a few pilot symbols is inserted into
the data symbol sequence at every fixed interval.
Alternatively, the length of the data symbols
and/or pilot symbols in each slot of the combined
25 symbol sequence may be one symbol length, or made
variable. Besides, there may be a slot consisting
- 25 -
of only the data symbols or pilot symbols. In
addition, the arrangement of the data symbols and
pilot symbols in each slot can be free.
Returning to Fig. 2A, the slot synchronization
5 detector 101 detects the position of the pilot
symbols in the combined symbol sequence at step "
S203.
Subsequently, at step S204, the pilot symbol
sequence acquisition section 112 and pilot block
10 generator 111 extract the pilot symbols from a
plurality of slots in a the combined symbol sequence,
and generates pilot blocks. Specifically, the pilot
symbol sequence acquisition section 112 acquires the
pilot symbols (sequence) from the plurality of slots
15 on the basis of the detection result at step S203,
and the pilot block generator 111 generates pilot
blocks from the pilot symbols acquired.
In the example as shown in Fig. 3, the pilot
symbols are extracted from the combined symbol
20 sequence over a range from the (n-K+l)-th slot to
the (n+K) -th slot, where K is a natural number and
is set at three in Fig. 3, to generate pilot blocks.
A pilot block is a set of the pilot symbols.
Although each pilot block is formed from all the
25 pilot symbols in a slot in the present embodiment,
it can be formed from part of the pilot symbols in
- 26 -
the slot. It is also possible to form one pilot
block from one pilot symbol. Besides, the number of
pilot symbols in a pilot block can be made variable
from slot to slot.
5 When obtaining the channel estimation values of
the data symbols in the n-th slot, it is not
essential to form the pilot blocks from nearly the
same numbers of the slots before and after the n-th
slots as in the example of Fig. 3. For example, the
10 pilot blocks can be generated only from the slots
with the number smaller than (previous to) the n-th
slot, considering the delay of the channel
estimation.
Through steps S205-S208, the channel estimation
15 value acquisition section 121 acquires the channel
estimation values of. the data symbols and pilot
symbols. First, at step S205, it averages the pilot
symbols <fj (estimated complex fading envelopes)
contained in each pilot block, thereby obtaining a
20 pilot block average value £ . This step is carried
out for all the pilot blocks (step S206) . When a
pilot block consists of only one pilot symbol, the
pilot symbol £ itself is adopted as the pilot block
average value In the example as shown in Fig. 3,
25 pilot block average values £ (n+i) are obtained for
- 27 -
the pilot blocks in the (n+i)-th slots, where i
varies from -K+l to K (K=3) .
At step S207, the channel estimation values £
of the data symbols and pilot symbols are obtained
by taking a weighted sum of the pilot block average
values £ weighted by the weighting factors a,
respectively. In the example of Fig. 3, the channel
estimation value ^ m (n) is obtained for the m-th data
symbol in the n-th slot with placing the weighting
factors of the (n+i)-th pilot blocks at CC m ,i.
In the present embodiment, the channel
estimation values are also obtained for the pilot
symbols to carry out the weighting control. The
channel estimation values are obtained in the same
manner as those of the data symbols. Specifically,
the channel estimation value t, (n)
is obtained for the m-th pilot symbol in the n-th
slot with placing the weighting factors of the
(n+i)-th pilot block at Om,i.
The channel estimation value £ m (n) is given by
the following equation (1) .
£ m (n) = Z ^,'|(n + i) (1)
i=-K+l
- 28 -
The foregoing step S2 07 is repeated for all the data
symbols and pilot symbols for which the channel
estimation values are to be obtained (step S2 08) .
It is also possible to use the same weighting
factors for all the data symbols and pilot symbols
in one slot to obtain the channel estimation values.
At step S209 after obtaining the channel
estimation values, the data symbol sequence
acquisition section 129 obtains the data symbol
sequence from the combined symbol sequence on the
basis of the detection result of the slot
synchronization detector 101.
At step S210, the data symbol sequence
compensator 13 0 compensates for the channel
fluctuations (fading phase fluctuations) of the data
symbol sequence using the channel estimation values
^ m (of the data symbols) obtained through steps
S203-S208. More specifically, it compensates for
the channel fluctuations of the data symbols by
multiplying the data symbol sequence by the complex
conjugates of the channel estimation values £ .
At step S211, the RAKE combiner 132 carries out
coherent combining of the compensated data symbol
sequences fed from respective RAKE fingers .
Fig. 4 is a flowchart illustrating a weighting
control processing by the CDMA receiver of the
present embodiment. At step S401, the pilot symbol
sequence compensator 146 compensates for the channel
fluctuations of the pilot symbol sequence using the
channel estimation values £ m (of the pilot symbols)
obtained through steps S203-S208.
At step S402, the error signal generator 142
generates an error signal (identification error
information) from the compensated pilot symbol
sequence and ideal pilot symbol sequence (which is
free from the channel fluctuations) . The ideal
pilot symbol sequence is known, and is prepared in
advance in the receiver 100.
At step S403, the weighting controller (MMSE)
144 controls the weighting (weighting factors a m ,i),
using the error signal and the pilot block average
values (the channel estimation values obtained from
individual pilot blocks) £ as feedback information.
Thus adaptively optimizing the weighting values
for the pilot symbols in response to the channel
fluctuation rate makes it possible to improve the
resistance to fading fluctuations, and to carry out
the highly accurate channel estimation.
[SECOND EMBODIMENT]
Fig. 5 is a block diagram showing a
configuration of a CDMA transceiver of a second
embodiment in accordance with the present invention.
The CDMA transceiver 500 of the present embodiment
transmits a signal including a combined symbol
sequence that has a plurality of slots and includes
data symbols and pilot symbols, and receives and
demodulates such a signal .
The CDMA transceiver 500 comprises a
transmitting processor 510 and a receiving processor
520. The configuration, receiving processing and
weighting control processing of the receiving
processor 520 are the same as the configuration
(Fig. 1), receiving processing (Figs. 2A and 2B) and
weighting control processing (Fig. 4) of the CDMA
receiver 100 of the first embodiment in accordance
with the present invention.
Fig. 6 is a block diagram showing a
configuration of the transmitting processor of the
CDMA transceiver in the second embodiment. As shown
in Fig. 6, the transmitting processor 510 comprises
a transmitting section 610, a channel encoder 622, a
combiner 630 and a spreader 627. Although in the
present embodiment, the channel encoder 622,
combiner 630 and the like are implemented by
software using a DSP (plus a memory for storing
programs) 620 as shown in Fig. 6, they can be
implemented by means of hardware.
Fig. 7 is a flowchart illustrating a
transmission processing by the transmitting
processor of the CDMA transceiver in the present
embodiment. First, at step S701, the channel
encoder 622 modulates (encodes) a data sequence,
thereby generating a data symbol sequence. At step
5702, the combiner 630 inserts pilot symbols into
each slot of the data symbol sequence, thereby
generating a combined symbol sequence. At step
5703, the spreader 627 spreads the combined symbol
sequence, thereby generating a transmitted signal
(spread combined symbol sequence). At step S704,
the transmitting section 610 transmits the
transmitted signal .
[THIRD EMBODIMENT]
Fig. 8 is a block diagram showing a CDMA
receiver of a third embodiment in accordance with
the present invention. The CDMA receiver 800 of the
present embodiment receives a signal including a
combined symbol sequence that has a plurality of
slots and contains data symbols and pilot symbols.
The CDMA receiver 800 comprises a receiving
section 810, a matched filter 825, a slot
synchronization detector 801, a pilot symbol
sequence acquisition section 812, a pilot block
5 generator 811, a channel estimation value
acquisition section 821, a data symbol sequence
acquisition section 829, a data symbol sequence
compensator 830, a RAKE combiner 832, a data
decision section 846, an error signal generator 842,
10 and a weighting controller (MMSE) 844. Although in
the present embodiment, the matched filter 825, slot
synchronization detector 801 and the like are
implemented by software using a DSP (plus a memory
for storing programs) 820 as shown in Fig. 8, they
15 can be implemented by means of hardware. The
configurations and functions of the receiving
section 810, matched filter 825 and the like are the
same as those of their counterparts in the CDMA
receiver 100 in the first embodiment in accordance
20 with the present invention. In addition, the CDMA
receiver 800 of the present embodiment carries out
the same processing as the receiving processing
(Figs. 2A and 2B) of the CDMA receiver 100 in the
first embodiment in accordance with the present
25 invention, except that it is unnecessary to obtain
- 33 -
the channel estimation values of the pilot symbols
in the present embodiment.
Fig. 9 is a flowchart illustrating a weighting
control processing by the CDMA receiver of the
present embodiment. At step S901, the error signal
generator 842 generates an error signal
(identification error information) from the
compensated data symbol sequence and from result
obtained by demodulating and deciding the
compensated data symbol sequence. The data decision
is carried out by the data decision section 846 that
makes a decision (0/1) of the output of the RAKE
combiner 832 .
At step S902, the weighting controller (MMSE)
844 carries out the control of weighting (weighting
factors a m ,i) using the error signal and the pilot
block average values (the channel estimation values
obtained from the individual pilot blocks) £ as the
feedback information.
Thus adaptively optimizing the weighting values
for the pilot symbols in response to the channel
fluctuation rate makes it possible to improve the
resistance to fading fluctuations, and to carry out
the highly accurate channel estimation.
Furthermore, since the weighting factors can be
updated not at the pilot symbol intervals (slot
intervals) but at the symbol intervals in the
present embodiment, the convergence capability of
5 the weighting factors can be improved.
Incidentally, a CDMA transceiver can be arranged
by employing the CDMA receiver 800 of the third
embodiment in accordance with the present invention
as the receiving processor, and the transmitting
10 processor 510 of the CDMA transceiver 500 of the
second embodiment in accordance with the present
invention as the transmitting processor.
[FOURTH EMBODIMENT]
15 Fig. 10 is a block diagram showing a CDMA
receiver of a fourth embodiment in accordance with
the present invention. The CDMA receiver 1000 of
the present embodiment receives and demodulates a
signal including a combined symbol sequence that has
2 0 a plurality of slots and includes both data symbols
and pilot symbols.
The CDMA receiver 1000 comprises a receiving
section 1010, a matched filter 1025, a slot
synchronization detector 1001, a pilot symbol
25 sequence acquisition section 1012, a pilot block
generator 1011, a channel estimation value
- 35 -
acquisition section 1021, a data symbol sequence
acquisition section 1029, a data symbol sequence
compensator 103 0, a RAKE combiner 1032, and a
weighting controller (inner product calculator)
5 1044. Although in the present embodiment, the
matched filter 1025, slot synchronization detector
1001 and the like are implemented by software using
a DSP (plus a memory for storing programs) 1020 as
shown in Fig. 10, they can be implemented by means
10 of hardware. The configurations and functions of
the receiving section 1010, matched filter 1025 and
the like are the same as those of their counterparts
of the CDMA receiver 100 of the first embodiment in
accordance with the present invention. Besides, the
15 CDMA receiver 1000 of the present embodiment carries
out the same processing as the receiving processing
(Figs. 2A and 2B) of the CDMA receiver 100 of the
first embodiment in accordance with the present
invention, except that it is unnecessary for the
20 CDMA receiver 1000 of the present embodiment to
obtain the channel estimation values of the pilot
symbols.
Fig. 11 is a flowchart illustrating a weighting
control processing by the CDMA receiver of present
25 embodiment. At step S1101, the weighting controller
(inner calculation) 1044 carries out the control
- 36 -
(updating) of the weighting (weighting factors (X m> i)
as the following equation (2), using the inner
products (correlation values) of the channel
estimation values £ of the data symbols and the
pilot block average values (channel estimation
values obtained from the individual pilot blocks) |
as the update values (feedback information) .
10
15
A m (n) = A m (n-i) + /l£ m (n)X(n)
f—
A m (n) =
a
m, -K+l
m, -K+2
0C m ^(n)
, X (n) =
« m .K-,(n)
« m . K (n)
£ m (n) = A' m (n-l) • X(n)
<?(n-K + l)
£(n-K + 2)
|(n + K-l)
^(n + K) j
(2)
where, A m (n) is the weighting factor of the m-th
data symbol in_the n-th slot, |i is a step size of
the updating, £ (n+i) is the pilot block average
value of the (n+i)-th slot, and £ m (n) is the channel
estimation value of the m-th data symbol in the n-th
- 37 -
slot. In addition, A' m (n) denotes the transpose of
A m (n) .
Thus adaptively optimizing the weighting values
for the pilot symbols in response to the channel
5 fluctuation rate makes it possible to improve the
resistance to fading fluctuations, and to carry out
the highly accurate channel estimation.
Furthermore, it is unnecessary for the present
embodiment to demodulate the data or to generate the
10 error signal, which makes it possible to carry out
the weighting control in response to the channel
fluctuations with a simple configuration.
Incidentally, a CDMA transceiver can be
configured by employing the CDMA receiver 1000 of
15 the fourth embodiment in accordance with the present
invention as the receiving processor, and the
transmitting processor 510 of the CDMA transceiver
500 of the second embodiment in accordance with the
present invention as the transmitting processor.
20
[FIFTH EMBODIMENT]
Fig . 12 is a block diagram showing a
configuration of the CDMA receiver of the fifth
embodiment in accordance with the present invention.
25 The CDMA receiver 1200 of the present embodiment
- 38 -
receives and demodulates a signal including a data
symbol sequence and a pilot symbol sequence parallel
to the data symbol sequence.
The CDMA receiver 1200 comprises a receiving
5 section 1210, a. data symbol sequence matched filter
1224, a pilot symbol sequence matched filter 122 6/ a
pilot block generator 1211, a channel estimation
value acquisition section 1221, a data symbol
sequence compensator 1230, a RAKE combiner 1232, an
10 error signal generator 1242, and a weighting
controller (MMSE) 1244.
Although in the present embodiment, the data
symbol sequence matched filter 1224, pilot symbol
sequence matched filter 1226 and the like are
15 implemented by software using a DSP (plus a memory
for storing programs) 1220 as shown in Fig. 12, they
can also be implemented by means of hardware.
Figs. 13A and 13B are flowcharts illustrating a
receiving processing by the CDMA receiver of the
20 present embodiment. First, at step S1301, the
receiving section 1210 receives a received signal,
that is, a spread data symbol sequence and a spread
pilot symbol sequence.
In the present embodiment, it is assumed that
25 the data symbol sequence and the pilot symbol
sequence are spread by a first spreading code and a
- 39 -
second spreading code, respectively, which are.
orthogonal to each other. However, it is also
possible to receive such data symbol sequence and
pilot symbol sequence that are spread by a first
spreading code and a second spreading code that are
not orthogonal to each other.
In addition, it is assumed in the present
embodiment that the spread data symbol sequence and
the spread pilot symbol sequence are impressed
(transmitted) on a first carrier and a second
carrier, respectively, which are orthogonal to each
other. However, it is also possible to receive such
data symbol sequence and pilot symbol sequence that
are impressed on a first carrier and a second
carrier that are not orthogonal to each other. As a
typical example of the carriers that are orthogonal
to each other, there are sine waves and cosine
waves .
At step S1302, the data symbol sequence matched
filter 1224 generates the data symbol sequence by
despreading the received signal using the first
spreading code. At step S1303, the pilot symbol
sequence matched filter 1226 generates the pilot
symbol sequence by despreading the received signal
using the second spreading code. Subsequently,
through steps S1304-S1308, the pilot block generator
1211 and channel estimation value acquisition
section 1221 carry out the channel estimation,
thereby obtaining the channel estimation values of
the data symbols and pilot symbols.
5 Fig. 14 is a diagram illustrating the operation
principle of the channel estimation by the channel
estimation unit of the present embodiment, taking an
example of obtaining the channel estimation value of
the n-th data symbol, where n is an integer. In the
10 example as shown in Fig. 14, the power of the pilot
symbol sequence is made less than that of the data
symbol sequence to suppress the power loss. In
addition, the data symbol sequence and pilot symbol
sequence are subjected to the transmission power
15 control at every slot interval .
Returning to Fig. 13A, the pilot block generator
1211 generates a plurality of pilot blocks from the
pilot symbol sequence at step S1304. In the example
as shown in Fig. 14, to generates L (three, in this
20 example) pilot blocks of X bits before and after the
n-th pilot symbol, pilot symbols from (n-K+l)-th to
(n+K)-th pilot symbol are used, where K is a natural
number equal to L x X.
It is preferable that the pilot blocks be formed
25 from pilot symbols belonging to many different slots
to use these pilot symbols for the channel
- 41 -
estimation. This is because although the pilot
symbols belonging to different slots have different
power, the effect of reduction in thermal noise and
interfering signals by using pilot symbols in more
5 slots is greater than the channel estimation error
caused by the power difference, and this enables
more highly accurate channel estimation. In the
example as shown in Fig. 14, six pilot blocks are
generated from pilot symbols belonging to seven
10 different slots.
It is not necessary, when obtaining the channel
estimation value of the n-th data symbol, to
generate the same number of pilot blocks before and
after the n-th pilot symbol as in the example of
15 Fig. 3. Thus, the pilot block can also be generated
only from the pilot symbols with the number less
than (previous to) the n-th pilot symbol,
considering the delay of the channel estimation.
The length of the pilot block can be determined
20 regardless of the length of the slot. In addition,
the length of the pilot block can be set equal to
the length of the pilot symbol. In other words, the
pilot block can consist of one pilot symbol.
Furthermore, the length of the pilot block may be
25 variable for each pilot block.
- 42 -
Through steps S1305-S1307, the channel
estimation value acquisition section 1221 obtains
the channel estimation values of the data symbols
and pilot symbols. First, at step S1305, it obtains
y\.
5 the pilot block average value £ by averaging the
y\
pilot symbols £ (estimated complex fading envelopes)
contained in the pilot block. It repeats the
processing for all the pilot blocks (step S1306) .
If the pilot block consists of a single pilot
yv
10 symbol, that pilot symbol £ itself becomes the pilot
y\
block average value £ . In the example of Fig. 14,
yv
the pilot block average values £ (m) are obtained
for respective i-th pilot blocks, where i varies
from -L to L and i*0 .
!5 At step S1307, the channel estimation value £ of
the data symbol or pilot symbol is obtained by
calculating the weighted sum of the pilot block
y\
average values £ . In the example of Fig. 14, the
channel estimation value £ (n) of the n-th data
20 symbol is obtained by setting the weighting factors
of the i-th pilot blocks as OCi .
In addition, in the present embodiment, the
channel estimation values are also obtained for the
pilot symbols to carry out the weighting control.
25 As the channel estimation value of the n-th pilot
- 43 -
symbol, the channel estimation value ^ (n) of the n-
th data symbol values can be used without any
change .
The channel estimation value £ (n) is given by
the following equation (3) .
|(n)= £ CXi-Idii) (3)
i=-L, i*0
The foregoing steps S1304-S1307 are repeated for
all data symbols and pilot symbols with which the
channel estimation values are to be obtained (step
S1308) .
After obtaining the channel estimation values,
the data symbol sequence compensator 1230
compensates for the channel fluctuations of the data
symbol sequence at step S1309 using the channel
estimation values £ (of the data symbols) . More
specifically, it compensates for the channel
fluctuations of the data symbols by multiplying the
data symbol sequence by the complex conjugates of
the channel estimation values £ .
At step S1310, the RAKE combiner 1232 carries
out the coherent combining of the compensated data
symbol sequences supplied from the RAKE fingers.
- 44 -
The CDMA receiver 12 00 of the present embodiment
carries out the same processing as the weighting
control processing (Fig. 4) by the CDMA receiver 100
in the first embodiment in accordance with the
5 present invention. In other words, the. pilot symbol
sequence compensator 1246 compensates for the
channel fluctuations of the pilot symbol sequence at
step S401 using the channel estimation values £ (of
the pilot symbols) .
10 At step S402, the error signal generator 1242
generates an error signal (identification error
information) from the compensated pilot symbol
sequence and the ideal pilot symbol sequence (which
is not affected by the channel fluctuations) . The
15 ideal pilot symbol sequence is known, and is
prepared in the receiver 1200 in advance.
At step S403, the weighting controller (MMSE)
1244 carries out the control of the weighting
(weighting factors (Xi) using the error signal and
2 0 the pilot block average values (channel estimation
values obtained from the individual pilot blocks) §
as the feedback information.
Thus adapt ively optimizing the weighting values
for the pilot symbols in response to the channel
25 fluctuation rate makes it possible to improve the
- 45 -
resistance to fading fluctuations, and to carry out
the highly accurate channel estimation.
[SIXTH EMBODIMENT]
5 Fig. 15 is a block diagram showing a
configuration of the CDMA transceiver of a sixth
embodiment in accordance with the present invention.
The CDMA transceiver 1500 of the present embodiment
transmits a signal including a data symbol sequence
10 and a pilot symbol sequence parallel to the data
symbol sequence, and receives and demodulates such a
signal.
The CDMA transceiver 1500 comprises a
transmitting processor 1510 and a receiving
15 processor 152 0. The configuration of the receiving
processor 1520 and its receiving processing and
weighting control processing are the same as the
configuration (see, Fig. 12), the receiving
processing (see, Figs. 13A and 13B) and weighting
20 control processing (see, Fig. 4) of. the CDMA
receiver 1200 of the fifth embodiment in accordance
with the present invention.
Fig. 16 is a block diagram showing a
configuration of the transmitting processor of the
25 CDMA transceiver of the present embodiment. As
shown in Fig. 16, the transmitting processor 1510
- 46 -
comprises a transmitting section 1610, a channel
encoder 1622, a data symbol sequence spreader 1626,
a pilot symbol sequence spreader 1628, and a
combiner 1630. Although in the present embodiment,
the channel encoder 1622, data symbol sequence
spreader 162 6 and the like are implemented by
software using a DSP (plus a memory for storing
programs) 1620, they can be implemented by means of
hardware .
Fig. 17 is a flowchart illustrating a
transmission processing by the transmitting
processor of the CDMA transceiver of the present •
embodiment. First, at step S1701, the channel
encoder 1622 generates a data symbol sequence by
modulating (encoding) a data sequence. At step
S1702, the data symbol sequence spreader 162 6
generates a spread data symbol sequence by spreading
the data symbol sequence using a first spreading
code. At step S1703, the pilot symbol sequence
spreader 1628 generates a spread pilot symbol
sequence by spreading the pilot symbol sequence
using a second spreading code. At step S1704, the
combiner 1630 combines the spread data symbol
sequence and the spread pilot symbol sequence,
thereby generating a transmitted signal. At step
- 47 -
S1705, the transmitting section 1610 transmits the
transmitted signal.
The present embodiment employs the first
spreading code and second spreading code which are
5 orthogonal to each other. However, the first and
second spreading codes can be used which are not
orthogonal to each other.
In addition, the present embodiment combines a
first carrier and a second carrier which are
10 orthogonal to each other after impressing the spread
data symbol sequence and the spread pilot symbol
sequence on the carries, and transmits the combined
carrier. However, first and second carriers which
are not orthogonal to each other can be combined
15 after impressing the spread data symbol sequence and
spread pilot symbol sequence thereon, so as to be
transmitted as the combined carrier.
[SEVENTH EMBODIMENT]
20 Fig. 18 is a block diagram showing a
configuration of the CDMA receiver of a seventh
'embodiment in accordance with the present invention.
The CDMA receiver 1800 of the present embodiment
receives and demodulates a signal including a data
25 symbol sequence and a pilot symbol sequence parallel
to the data symbol sequence.
- 48 -
The CDMA receiver 1800 comprises a receiving
section 1810, a data symbol sequence matched filter
1824, a pilot symbol sequence matched filter 1826, a
pilot block generator 1811, a channel estimation
value acquisition section 1821, a data symbol
sequence compensator 1830, a RAKE combiner 1832, a
data decision section 1846, an error signal
generator 1842, and a weighting controller (MMSE)
1844. Although in the present embodiment, the data
symbol sequence matched filter 1824, pilot symbol
sequence matched filter 182 6 and the like are
implemented by software using a DSP (plus a memory
for storing programs) 1820 as shown in Fig. 18, they
can also be implemented by means of hardware. The
receiving section 1810, data symbol sequence matched
filter 1824 and the like have the same
configurations and functions as those of their
counterparts of the CDMA receiver 1200 of the fifth
embodiment in accordance with the present invention.
In addition, the CDMA receiver 1800 of the present
embodiment carries out the same processing as the
receiving processing of the CDMA receiver 1200 (see,
Fig. 13A and 13B) of the fifth embodiment in
accordance with the present invention, except that
it is unnecessary for the present embodiment to
- 49 -
obtain the channel estimation values of the pilot
symbols .
Furthermore, the CDMA receiver 1800 of the
present embodiment carries out the same processing
5 as the weighting control processing of the CDMA
receiver 800 (see, Fig. 9) of the third embodiment
in accordance with the present invention.
Specifically, at step S901, the error signal
generator 1842 generates an error signal
10 (identification error information) from the
compensated data symbol sequence and from the result
obtained by demodulating and deciding the
compensated data symbol sequence. The data decision
is carried out by the data decision section 1846
15 that makes a decision (0/1) of the output of the
RAKE combiner 1832.
At step S902, the weighting controller (MMSE)
1844 carries out the control of the weighting
(weighting factors (Xi) using the error signal and
20 pilot block average values (channel estimation
values obtained from the individual pilot blocks) §
as the feedback
information.
Thus adaptively optimizing the weighting values
25 for the pilot symbols in response to the channel
- 50 -
fluctuation rate makes it possible to improve the
resistance to fading fluctuations, and to carry out
the highly accurate channel estimation.
Incidentally, a CDMA transceiver can be arranged
by employing the CDMA receiver 1800 of the seventh
embodiment in accordance with the present invention
as the receiving processor, and the transmitting
processor 1510 of the CDMA transceiver 1500 of the
sixth embodiment in accordance with the present
invention as the transmitting processor.
[EIGHTH EMBODIMENT]
Fig. 19 is a block diagram showing a
configuration of a CDMA receiver of an eighth
embodiment in accordance with the present invention.
The CDMA receiver 1900 of the present embodiment
receives and demodulates a data symbol sequence and
a pilot symbol sequence parallel to the data symbol
sequence .
The CDMA receiver 1900 comprises a receiving
section 1910, a data symbol sequence matched filter
1924, a pilot symbol sequence matched filter 1926, a
pilot block generator 1911, a channel estimation
value acquisition section 1921, a data symbol
sequence compensator 1930, a RAKE combiner 1932, and
a weighting controller (inner product calculation)
1944. Although in the present embodiment, the data
symbol sequence matched filter 1924, pilot symbol
sequence matched filter 1926 and the like are
implemented by software using a DSP (plus a memory
5 for storing programs) 1920 as shown in Fig. 19, they
can be implemented by means of hardware. The
receiving section 1910, data symbol sequence matched
filter 1924 and the like have the same
configurations and functions as their counterparts
10 of the CDMA receiver 12 00 of the fifth embodiment in
accordance with the present invention. Besides, the
CDMA receiver 1900 of the present embodiment carries
out the same receiving processing as the CDMA
receiver 1200 (see, Figs. 13A and 13B) of the fifth
15 embodiment in accordance with the present invention,
except that it is unnecessary for the present
embodiment to obtain the channel estimation values
of the pilot symbols.
Furthermore, the CDMA receiver 1900 of the
20 present embodiment carries out the same weighting
control processing as the CDMA receiver 1000 (see,
Fig. 11) of the fourth embodiment in accordance with
the present invention. Specifically, at step S1101,
the weighting controller (inner product calculation)
25 1944 carries out the control (updating) of the
weighting (weighting factors a±) using the inner
- 52 -
products (correlation values) of the channel
estimation values £ of the data symbols values and
the pilot block average values (channel estimation
values obtained from individual pilot blocks) | as
the updating values (feedback information) as
expressed by the following equation (4) .
A(n) = A(n-l) + \L \ (n) X (n)
r«- L (n)
A(n) =
a.,(n)
«,(n)
f—
, X (n) =
v a L (n) j
5(n) = A'(n-l) • X(n)
£(n. L )
I(n.)
(4)
10
where, A(n) is the weighting factor of the n-th data
symbol, u is a step size of the updating, £ (ni) is
the pilot block average value of the i-th pilot
block, and § (n) is the channel estimation value of
- 53 -
the n-th data symbol. In addition, A fc (n) denotes the
transpose of A(n) .
Thus adaptively optimizing the weighting values
for the pilot symbols in response to the channel
fluctuation rate makes it possible to improve the
resistance to fading fluctuations, and to carry out
the highly accurate channel estimation."
Furthermore, it is unnecessary for the present
embodiment to demodulate the data or to generate the
error signal, which makes it possible to carry out
the weighting control in response to the channel
fluctuations with a simple configuration.
Incidentally, a CDMA transceiver can be
configured by employing the CDMA receiver 1900 of
the eighth embodiment in accordance with the present
invention as the receiving processor, and the
transmitting processor 1510 of the CDMA transceiver
1500 of the sixth embodiment in accordance with the
present invention as the transmitting processor.
[SUPPLEMENTS]
Fig. 20 is a diagram illustrating
characteristics of a required error rate (BER=10 -3 )
versus the product of a maximum Doppler frequency
(fd) and a slot time (T s i 0 t) under a two-path
Rayleigh model. Fig. 20 illustrates characteristics
(TM_P) associated with the CDMA receiver of the
fourth embodiment in accordance with the present
invention (time multiplexed pilot channel method),
characteristics (Para_P) associated with the CDMA
receiver of the eighth embodiment in accordance with
the present invention (parallel pilot channel
method) , characteristics (TM_C) associated with the
conventional CDMA receiver with the fixed weighting
factors (time multiplexed pilot channel method) , and
characteristics (Para_C) associated with the
conventional CDMA receiver with the fixed weighting
factors (parallel pilot channel method ) .
Fig. 21 is a diagram illustrating BER
characteristics under a Vehicular-B environment when
fdT s lot=0. 003125 and fdT s lot=0 . 28 , and Fig. 22 is a
diagram illustrating characteristics of a required
error rate (BER=10"3) versus fdT s iot under the
Vehicular-B environment.
It is found from Figs. 20 and 22 that both the
CDMA receivers of the fourth and eighth embodiments
in accordance with the present invention have an
improvement of about 0.2 dB under the two-path
Rayleigh model and of about 0.4 dB under the
Vehicular-B environment in a low rate fading as
compared with the conventional CDMA receiver, and
- 55 -
that the improvement increases with the fading rate
in a high rate fading. Here, the improvement under
the Vehicular-B environment is greater than that
under the two-path Rayleigh model low rate fading
5 because the present invention has a greater
improvement when it can use more pilot symbols as in
the Vehicular-B environment in which the effect of
noise is greater during the low fading.
Furthermore, it is thought that the time
10 multiplexed pilot channel method (the CDMA receiver
of the fourth embodiment in accordance with the
present invention) and the parallel pilot channel
method (the CDMA receiver of the eighth embodiment
in accordance with the present invention) have
15 little difference over the entire range from the low
rate to high rate fading. This is because in the
low rate, the energy used for the estimation is
equal, and the fading fluctuations are small, and
because in the high rate, the effect characteristic
20 of the time multiplexed pilot channel method that
the signal energy is obtained in a short time is
nearly comparable to the improvement of the parallel
pilot channel method in the traceability to the high
rating fading owing to a reduction in the number of
25 synchronization additions of the parallel pilot
- 56 -
channel method as compared with the time multiplexed
pilot channel method.
As described above, the present invention can
improve the resistance to fading fluctuations and
carry out the highly accurate channel estimation by
adaptively optimizing the weighting values for the
pilot symbols in response to the rate of channel
fluctuations.
Achieving the highly accurate channel estimation
and the compensation for the channel fluctuations of
the data symbols based on the estimation makes it
possible to implement the absolute phase decision
for each data symbol using the coherent detection
even under the Rayleigh fading environment, for
example, and hence to reduce the SNIR required for
obtaining a required reception quality (received
error rate) . This can reduce the transmission power
and increase the capacity of the system in terms of
the number of users .
- 57 -
WHAT IS CLAIMED IS:
1. A CDMA receiver for receiving and demodulating a
signal including a combined symbol sequence that has
5 a plurality of slots and includes data symbols and
pilot symbols, said CDMA receiver comprising:
means for detecting positions of the pilot
symbols in the combined symbol sequence;
means for generating pilot blocks by extracting
10 in a plurality of slots the pilot symbols from the
combined symbol sequence in response to a result of
the detection;
means for obtaining channel estimation values by
calculating a weighted sum of average values of the
15 pilot symbols in the pilot blocks;
means for acquiring from the combined symbol
sequence a data symbol sequence in accordance with
the result of the detection;
means for compensating for channel fluctuations
20 of the data symbol sequence using the channel
estimation values; and
means for controlling the weighting in response
to a rate of the channel fluctuations.
25 2. The CDMA receiver as claimed in claim 1, wherein
said means for controlling the weighting comprises:
- 58 -
means for compensating for, using the channel
estimation values, channel fluctuations of a pilot
symbol sequence extracted from the combined symbol
sequence;
means for generating an error signal from the
compensated pilot symbol sequence and an ideal pilot
symbol sequence; and
means for carrying out the weighting control
using the error signal and the average values of the
pilot symbols included in the pilot blocks.
3. The CDMA receiver as claimed in claim 1, wherein
said means for controlling the weighting comprises:
means for generating an error signal from the
compensated data symbol sequence and from result
obtained by demodulating and deciding the
compensated data symbol sequence; and
means for carrying out the weighting control
using the error signal and the average values of the
pilot symbols included in the pilot blocks.
4. The CDMA receiver as claimed in claim 1, wherein
said means for controlling the weighting carries out
the weighting control using as update values inner
products of the channel estimation values of the
data symbols and the average values of the pilot
symbols included in the pilot blocks.
5. The CDMA receiver as claimed in any one of
claims 1-4, wherein said CDMA receiver receives a
signal including a combined symbol sequence -having a
frame structure consisting of slots in which the
pilot symbols consisting of a few symbols are
inserted into the data symbol sequence at every
fixed interval.
6. The CDMA receiver as claimed in any one of
claims 1-5, wherein the pilot blocks are formed from
all the pilot symbols in a slot.
7 . The CDMA receiver as claimed in any one of
claims 1-6, wherein when obtaining the channel
estimation value of a data symbol in an n-th slot of
the combined symbol sequence, where n is an integer,
the pilot blocks are generated from an (n-K+l)-th
slot to an (n+K)-th slot of the combined symbol
sequence, where K is a natural number.
8. A CDMA receiver for receiving and demodulating a
signal including a data symbol sequence and a pilot
- 60 -
symbol sequence parallel to the data symbol
sequence, said CDMA receiver comprising:
means for generating a plurality of pilot blocks
from the pilot symbol sequence;
means for obtaining channel estimation values by
calculating a weighted sum of average values of the
pilot symbols in the pilot blocks;
means for compensating for channel fluctuations
of the data symbol sequence using the channel
estimation values; and
means for controlling the weighting in response
to a rate of the channel fluctuations .
9 . The CDMA receiver as claimed in claim 8 , wherein
said means for controlling the weighting comprises:
means for compensating for, using the channel
estimation values, channel fluctuations of the pilot
symbol sequence;
means for generating an error signal from the
compensated pilot symbol sequence and an ideal pilot
symbol sequence; and
means for carrying out the weighting control
using the error signal and the average values of the
pilot symbols included in the pilot blocks.
10. The CDMA receiver as claimed in claim 8,
wherein said means for controlling the weighting
comprises :
means for generating an error signal from the
compensated data symbol sequence and from result
obtained by demodulating and deciding the
compensated data symbol sequence; and
means for carrying out the weighting control
using the error signal and the average values of the
pilot symbols included in the pilot blocks.
11. The CDMA receiver as claimed in claim 8,
wherein said means for controlling the weighting
carries out the weighting control using as update
values inner products of the channel estimation
values of the data symbols and the average values of
the pilot symbols included in the pilot blocks.
12 . The CDMA receiver as claimed in any one of
claims 8-11, wherein said CDMA receiver receives a
signal including a data symbol sequence which is
spread using a first spreading code, and a pilot
symbol sequence which is parallel to the data symbol
sequence and spread using a second spreading code,
the first spreading code and the second spreading
code being orthogonal to each other.
- 62 -
13. The CDMA receiver as claimed in any one of
claims 8-12, wherein said CDMA receiver receives a
signal including a spread data symbol sequence which
is impressed on a first carrier, and a spread pilot
symbol sequence which is parallel to the data symbol
sequence and is impressed on a second carrier, the
first carrier and the second carrier being
orthogonal to each other.
14. The CDMA receiver as claimed in any one of
claims 8-13, wherein when obtaining the channel
estimation value of an n-th data symbol in the data
symbol sequence, where n is an integer, the
plurality of pilot blocks are generated from an (n-
K+l)-th pilot symbol to an (n+K) -th pilot symbol in
the pilot symbol sequence, where K is a natural
number .
15. The CDMA receiver as claimed in any one of
claims 8-14, wherein the plurality of pilot blocks
have a same length.
16. A CDMA transceiver including a transmitting
section for transmitting a signal including a
combined symbol sequence that has a plurality of
- 63 -
slots and includes data symbols and pilot symbols,
and a receiving section for receiving and
demodulating the signal, said receiving section
comprising:
means for detecting positions of the pilot
symbols in the combined symbol sequence;
means for generating pilot blocks by extracting,
in a plurality of slots, the pilot symbols from the
combined symbol sequence in response to a result of
the detection;
means for obtaining channel estimation values by
calculating a weighted sum of average values of the
pilot symbols included in the pilot blocks;
means for acquiring from the combined symbol
sequence a data symbol sequence in accordance with
the result of the detection;
means for compensating for channel fluctuations
of the data symbol sequence using the channel
estimation values; and
means for controlling the weighting in response
to a rate of the channel fluctuations.
17. A CDMA transceiver including a transmitting
section for transmitting a signal including a data
symbol sequence and a pilot symbol sequence parallel
to the data symbol sequence, and a receiving section
- 64 -
for receiving and demodulating the signal, said
receiving section comprising:
means for generating a plurality of pilot blocks
from the pilot symbol sequence;
means for obtaining channel estimation values by
calculating a weighted sum of average values of the
pilot symbols in the pilot blocks;
means for compensating for channel fluctuations
of the data symbol sequence using the channel
estimation values; and
means for controlling the weighting in response
to a rate of the channel fluctuations.
18. A CDMA receiving method of receiving and
demodulating a signal including a combined symbol
sequence that has a plurality of slots and includes
data symbols and pilot symbols, said CDMA receiving
method comprising the steps of:
detecting positions of the pilot symbols in the
combined symbol sequence;
generating pilot blocks by extracting, in a
plurality of slots, the pilot symbols from the
combined symbol sequence in response to a result of
the detection;
- 65 -
obtaining channel estimation values by
calculating a weighted sum of average values of the
pilot symbols in the pilot blocks;
acquiring from the combined symbol sequence a
data symbol sequence in accordance with the result
of the detection; and
compensating for channel fluctuations of the
data symbol sequence using the channel estimation
value,
wherein the weighting is controlled in response
to a rate of the channel fluctuations.
19 . A CDMA receiving method of receiving and
demodulating a signal including a data symbol
sequence and a pilot symbol sequence parallel to the
data symbol sequence, said CDMA receiving method
comprising the steps of:
generating a plurality of pilot blocks from the
pilot symbol sequence;
obtaining channel estimation values by
calculating a weighted sum of average values of the
pilot symbols in the pilot blocks; and
compensating for channel fluctuations of the
data symbol sequence using the channel estimation
value,
- 66 -
wherein the weighting is controlled in response
to a rate of the channel fluctuations.
- 67 -
ABSTRACT OF THE DISCLOSURE
A CDMA receiver and a CDMA transceiver are
provided which have high resistance to fading
fluctuations, and carry out highly accurate channel
estimation, considering the rate of channel
fluctuations. When carrying out the channel
estimation by calculating weighted sums of the
(average values of) pilot symbols interposed into a
data symbol sequence, the weighting control is
performed considering the rate of the channel
fluctuations. For example, the weighting control is
carried out using, as its update values, inner
products of the channel estimation values and the
(average values of) pilot symbols. This makes it
possible to achieve the highly accurate channel
estimation .
- 68 -
2/25
( START )
RECEIVE RECEIVED SIGNAL
(SPREAD COMBINED SYMBOL SEQUENCE)
GENERATE COMBINED SYMBOL
SEQUENCE BY DESPREADING
RECEIVED SIGNAL
T
DETECT POSITIONS OF PILOT SYMBOLS IN
COMBINED SYMBOL SEQUENCE
GENERATE PILOT BLOCKS BY EXTRACTING PILOT
SYMBOLS FROM COMBINED SYMBOL SEQUENCE
IN PLURALITY OF SLOTS
OBTAIN PILOT BLOCK AVERAGE VALUE BY
AVERAGING PILOT SYMBOLS INCLUDED IN
PILOT BLOCK
FIG2
S201
S202
S203
S204
S205
S206
OBTAIN PILOT BLOCK AVERAGES FOR
ALL PILOT BLOCKS?
NO
FIG.2A
3/25
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EACH OF DATA SYMBOLS AND PILOT SYMBOLS
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S207
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( END )
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f
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f
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S1301
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S1307
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17/25
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1510
TRANSMUTING PROCESSOR
1520
RECEIVING PROCESSOR
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18/25
19/25
( START )
GENERATE DATA SYMBOL SEQUENCE BY
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GENERATE SPREAD DATA SYMBOL
SEQUENCE BY SPREADING DATA
SYMBOL SEQUENCE
GENERATE SPREAD PILOT SYMBOL
SEQUENCE BY SPREADING PILOT
SYMBOL SEQUENCE
i
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SYMBOL SEQUENCE
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S1701
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( END )
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(54)Title: CDMA RECEIVER AND CDMA TRANSMITTER/RECEIVER
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WO 99/55033 PCT/JP99/02154
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1 : "Rayleigh Fading Compensation for QAM in Land Mobile Radio
Communication: Seiichi Sampei and Terumi Sunaga, IEEE Trans. Vehicular
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2 : "Channel Estimation Filter Using Time-Multiplexed Pilot
Channel for Coherent RAKE Combining in DS-CDMA Mobile Radio:
Hidehiro Ando et.al, IEICE Trans. Commun. V0I.8I-B, No.7, July 1998"T*
1112 311, XK2K:J:*f-ir*JHtjgo*jtfc*tHT?*4. -O^S
WO 99/55033 PCT/JP99/02154
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3 I "Performance Comparison between Time-Multiplexed Pilot
Channel and Parallel Pilot Channel for Coherent Rake Combining in
DS-CDMA Mobile Radio: Sadayuki Abeta et.al, IEICE Trans. Commun.
V0I.8I-B, No.7, July 1998"-C-Ii, * > */l/«Jg*fir 3 IB
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Xlfc 4 : "DS/CDMA Coherent Detection System with a Suppressed Pilot
Channel: Sadayuki Abetaet.al, IEEE GLOBECOM'94, pp. 1622-1626, 1994"
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